Compile error on transposing a dense matrix in Spark MLlib

Question

I'm trying to create a dense matrix in Spark and then transpose it using the following code:

val weightsMatrix = Matrices.dense(1, 3, Array.fill[Double](3)(0))

val weightsMatrix_t = weightsMatrix.transpose()

but it fails with the compilation error below.

not enough arguments for method apply: (i: Int, j: Int)Double in 
trait Matrix.
[error] Unspecified value parameters i, j.
[error]     val weightsMatrix_t = weightsMatrix.transpose()
[error]                                                  ^
[error] one error found
[error] (compile:compileIncremental) Compilation failed

I've checked in the documentation that the function transpose does not take any parameters, but it seems a method named apply is somehow involved.

Answer 1

The apply is referring to the () trialing your transpose. Transpose is a member variable of matrix so when you call tanspose it is returning a matrix and you are then calling an index on that matrix with no index values given. the solution is

val weightsMatrix_t = weightsMatrix.transpose

without the ()